Ohad Goldbart

Nanocompression of individual multilayered polyhedral nanoparticles

Inorganic layered materials can form hollow multilayered polyhedral nanoparticles. The size of these multi-wall quasi-spherical structures varies from 4 to 300 nm. These materials exhibit excellent tribological and wear-resisting properties. Measuring and evaluating the stiffness of individual nanoparticle is a non-trivial problem. The current paper presents an in situ technique for stiffness measurements of individual WS(2) nanoparticles which are 80 nm or larger using a high resolution scanning electron microscope (HRSEM). Conducting the experiments in the HRSEM allows elucidation of the compression failure strength and the elastic behavior of such nanoparticles under uniaxial compression.

Radial compression studies of WS2 nanotubes in the elastic regimea)

Multiwalled nanotubes and nanoparticles of metal dichalcogenides express unique mechanical and tribological characteristics. A widely studied member of this class of materials is the WS2 nanotube whose structure consists of layers of covalent W-S bonds joined by the van der Waals interactions between the sulfur layers which mediate any interlayer sliding or compression. One of the intriguing aspects of these structures is the response of these layers under mechanical stress. Such internal degrees of freedom can profoundly impact on the overall mechanical response. The fact that the internal structure of these nanotubes is well characterized enables a full treatment of the problem. Here, the authors report an experimental and modeling study of the radial mode of deformation. Three independent atomic force microscope experiments were employed to measure the nanomechanical response using both large (radius=100 nm) and small (radius=3–15 nm) probe tips. Two different analytical models were applied to analyze ...

Experimental, finite element, and density-functional theory study of inorganic nanotube compression

Interactions between the walls in multiwalled nanotubes are key to determining their mechanical properties. Here, we report studies of radial deformation of multiwalled WS2 nanotubes in an atomic force microscope. The experimental results were fitted to a finite element model to determine the radial modulus. These results are compared with density-functional tight-binding calculations of a double-walled tube. Good agreement was obtained between experiment and calculations. The results indicate the importance of the sliding between layers in moderating the radial modulus. A plateau in the deformation curves is seen to have atomistic origins.

Lubricating Medical Devices with Fullerene-Like Nanoparticles

In the present work, MoS2 nanoparticles with fullerene-like structure, and most particularly those doped with minute amounts of rhenium atoms, are used as additive to medical gels in order to facilitate their entry into constricted openings of soft material rings. This procedure is used to mimic the entry of endoscopes to constricted openings of the human body, like urethra, etc. It is shown that the Re-doped nanoparticles reduce the traction force used to retrieve the metallic lead of the endoscope from the soft ring by a factor close to three times with respect to the original gel. The mechanism of the mitigation of both friction and adhesion forces in these systems by the nanoparticles is discussed.

Diameter-dependent wetting of tungsten disulfide nanotubes

Significance The wetting of solid surfaces by liquids is of great interest in scientific fields ranging from lubrication to the strength of composite materials. These interactions can change dramatically at the nanoscale, impacting on current development of novel devices and materials. We have studied the wetting of individual, size-selected tungsten disulfide nanotubes, both experimentally and theoretically. The results show that wetting forces and free energy can vary by orders of magnitude when capillary action is enhanced in open-ended vs. closed-ended nanotubes, as deduced from the influence of specific nanotube size and geometry in governing the final wetting properties. This work provides a comprehensive view of the molecular-level interactions involved in nanotube wetting. The simple process of a liquid wetting a solid surface is controlled by a plethora of factors—surface texture, liquid droplet size and shape, energetics of both liquid and solid surfaces, as well as their interface. Studying these events at the nanoscale provides insights into the molecular basis of wetting. Nanotube wetting studies are particularly challenging due to their unique shape and small size. Nonetheless, the success of nanotubes, particularly inorganic ones, as fillers in composite materials makes it essential to understand how common liquids wet them. Here, we present a comprehensive wetting study of individual tungsten disulfide nanotubes by water. We reveal the nature of interaction at the inert outer wall and show that remarkably high wetting forces are attained on small, open-ended nanotubes due to capillary aspiration into the hollow core. This study provides a theoretical and experimental paradigm for this intricate problem.

New Deposition Technique for Metal Films Containing Inorganic Fullerene-Like (IF) Nanoparticles

This study describes a new method for fabrication of thin composite films using physical vapor deposition (PVD). Titanium (Ti) and hybrid films of titanium containing tungsten disulphide nanoparticles with inorganic fullerene-like structure (Ti/IF-WS2) were fabricated with a modified PVD machine. The evaporation process includes the pulsed deposition of IF-WS2 by a sprayer head. This process results in IF-WS2 nanoparticles embedded in a Ti matrix. The layers were characterized by various techniques, which confirm the composition and structure of the hybrid film. The Ti/IF-WS2 shows better wear resistance and a lower friction coefficient when compared to the Ti layer or Ti substrate. The Ti/IF films show very good antireflective properties in the visible and near-IR region. Such films may find numerous applications, for example, in the aerospace and medical technology.